1. Field of the Invention
The invention relates to capillary coating devices and methods, and more particularly to capillary coating devices and methods for manufacturing color filters of liquid crystal displays, color units of fluorescent layers of plasma displays, biomedical products, flexible electronic members, or cells.
2. Description of the Related Art
A flat panel display has been developed to replace a cathode-ray tube display. The flat panel display, such as a liquid crystal display, comprises a backlight source, a polarizer, a glass substrate, a liquid crystal panel, a thin-film transistor (TFT), and a color filter (CF). Specifically, the color filter plays an important role in exhibition of colored characteristics and contrast of the liquid crystal display.
The color filter of the liquid crystal display and a color unit of a fluorescent layer of a plasma display are critical components for transforming black-and-white images into colored images. For the color filter of the liquid crystal display, multiple red, green, and blue pixels are arranged on the glass substrate and every three of the pixels correspond to a pixel on the liquid crystal display. After white light passes through the red, green, and blue pixels, three primary colors, red (R), green (G), and blue (B) colors, are generated. By a grayscale effect generated by liquid crystal molecules, the three primary colors mix with each other to form diverse colors. Currently, the color filter may be manufactured using five methods, i.e. exposure development, stamping, ink-jet printing, stripe coating, and discontinuous micro-patch coating methods. As to the exposure development method, a pattern is defined by repeated coating of a flat liquid film and exposure/development steps. The exposure development method may be divided into many sub-methods including dyeing, pigment dispersion, electro deposition, etc. As to the stamping method, a stamp defines a pattern and pigments are imprinted on a substrate. As to the ink-jet printing method, a nozzle spouts tiny drops over a substrate, forming micro-patch patterns. As to the stripe coating method, various pigments are coated on a black matrix of a color filter in a stripe shape. As to the discontinuous micro-patch coating method, a discontinuously supplied fluid directly defines a micro-patch pattern.
In the aforementioned exposure development methods, coating of the flat liquid film must be provided in advance. The coating process comprises spin coating, extrusion spin coating, and slot patch coating process. For the spin coating process, such as that disclosed in U.S. Pat. No. 4,451,507, utilization of raw materials is not thorough. However, for the extrusion spin coating process (as disclosed by U.S. Pat. No. 6,191,053) and slot patch coating process (as disclosed by U.S. Pat. No. 4,938,994), utilization of the raw materials can be enhanced. As to the sub-methods of dyeing, pigment dispersion, and electro deposition, raw materials for coating the liquid film are different, thereby causing differences in manufacturing processes.
As to the dyeing method, as disclosed in U.S. Pat. No. 4,744,635, a transparent and organic sensitive material serves as an absorptive layer and a pattern is processed by a litho/etching technique. The absorptive layer is then immersed in a dye solution to be dyed. To obtain the pattern with red (R), green (G), and blue (B) colors, the aforementioned process must be performed by triple coating, exposure, dyeing, roast, and anti-dyeing steps. Accordingly, as the dyeing method provides complex steps and requires expensive instruments or equipment and the heat-resistant and light-resistant properties of dyes are poor, the dyeing method is limited to manufacture of small liquid crystal display panels and cathode-ray tubes.
The pigment dispersion method, as disclosed in U.S. Pat. Nos. 5,085,973 and 4,786,148, is commonly used to manufacture the color filters. The pigment dispersion method employs sensitive and heat-hardened pigments and comprises the following steps: coating a coloring material on a glass substrate; performing exposure, development, and roast operations to form a monochromatic patch; and repeatedly performing exposure, development, and roast operations to form R, G, and B pixels. Nevertheless, the pigment dispersion method provides complex steps and requires expensive equipment, utility rate of the coloring material is low, and variability of the pixels and pattern is poor. Accordingly, the pigment dispersion method cannot be applied to manufacture of large panels and conform to low-price demands.
As to the electro deposition method, as disclosed in U.S. Pat. No. 4,522,691, a transparent and patterned conductive film is formed on a glass substrate and a film formed of a coloring material is formed on the transparent and patterned conductive film using an electrophoresis technique. After the aforementioned process is repeated three times, a pattern with R, G, and B colors can be obtained. Nevertheless, as the electro deposition method requires many processing parameters, productivity cannot be easily controlled. Specifically, because of the transparent and patterned conductive film, light permeability and definition of the pattern is insufficient. Additionally, arrangement of the pattern is limited, such that a color filter with a complicated pattern cannot be produced.
Regarding the exposure development method, as the pattern cannot be directly defined during coating and excessive raw materials must be removed by an exposure/development step, utility rate of the raw materials is less than one-third. Thus, the exposure development method cannot be applied to mass production and conform to reduction of manufacturing costs.
As to the stamping method, as disclosed in Taiwan Patent No. 535010, a stamp or a printing board with a micro-structural pattern is stained with a dye and is stamped on a substrate, forming the micro-structural pattern thereon. The micro-structural pattern is then roasted. After the aforementioned process is repeated three times, a pattern with R, G, and B colors can be obtained. Although the stamping method can enhance the utility rate of the raw materials and reduce the manufacturing costs, variability of the pattern is still insufficient. Accordingly, arrangement of pixels cannot be randomly changed.
As to the ink-jet printing method, as disclosed in Taiwan Patent No. 512242, a pattern can be determined by directly controlling the position of nozzles. The ink-jet printing method comprises the following steps: coating an absorptive layer on a glass substrate, securing ink drops to the glass substrate; and spouting red, green, and blue ink over the glass substrate with the nozzles, forming a required pattern. By using the inkjet printing method, utility rate of raw materials and variability of the pattern are promoted. Each ink drop must be accurately spouted over a micrometer-size area or an area with a smaller size. Nevertheless, as airflows easily interfere with flight of the ink drops, the ink drops are often spouted over other patches, contaminating the other patches. Thus, a machine required for spouting the ink drops must provide high positioning precision and the moving speed thereof is limited. Moreover, each nozzle can spout only one ink drop at a time, such that the productivity cannot be enhanced. To solve the aforementioned problem, the number of the nozzles must be increased, thereby causing increased manufacturing costs. When ink-spouting operation is performed, all the nozzles must be maintained in a good condition and must not be obstructed. When the inkjet printing method is applied to manufacture of the large panels, the size of the machine required for spouting the ink drops is enlarged and mobility and uniformity of the machine must be maintained.
The stripe coating method is an improved slot coating method. As to the stripe coating method, various pigments are coated on a black matrix in the form of stripes, forming R, G, and B stripes. For example, U.S. Pat. No. 6,423,140 discloses a slot coating method using multiple guiding plates for a coating mold. Stripes composed of three fluids can be obtained using the slot coating method. Specifically, the three fluids are input to multiple channels of the coating mold via three inlets thereof. The three fluids gather on one side through the guiding plates, forming the stripes. Nevertheless, the coating mold must be provided with high precision. Additionally, flow of the three fluids is not easily controlled, thereby causing mixing therebetween. Moreover, Taiwan Patent Publication No. 200702743 discloses a stripe coating method and mechanism for manufacturing the color filter. The stripe coating mechanism comprises a coating mold with multiple tiny outlets arranged in a single row. A fluid flows into the coating mold. By relatively moving a coating substrate, multiple parallel monochromatic stripes are coated on the color filter. Nevertheless, as the coating mold is provided with various channels for generating the stripes, resistance caused by the fluid is significantly high. Thus, a fluid supply source must be provided in the stripe coating mechanism to transport the fluid. Moreover, as the profile of the channels in the coating mold is fixed, the gaps between the coated parallel stripes are fixed, resulting in low variability of a pattern.
Taiwan Patent Publication No. 200824799 and U.S. Patent Publication No. 20080145537 disclose a discontinuous micro-patch coating device. Continuous coating operation and a discontinuously supplied fluid define a micro-patch pattern. The discontinuously supplied fluid is a micro multi-phase fluid composed of multiple primary fluids and a secondary fluid. The coating operation is performed by the primary fluids. The secondary fluid cuts off the primary fluids and may comprise a gas. By controlling the volume and length of the primary and secondary fluids, the micro-patch pattern can be controlled. Nevertheless, as the aforementioned coating operation requires a plurality of fluid supply sources and the flow of the fluids must be precisely controlled, overall control of the coating operation is complex and equipment costs are relatively high.
Hence, there is a need for a capillary coating device and method, solving the aforementioned problems.